Surface acoustic wave testing

Most SAW transducers are inadequate for operation in liquids because most types of surface acoustic waves are completely damped in this viscous environment. Therefore, QCM transducers are used instead. For successful operation of an MIP-QCM chemosensor in liquid, the MIP film should be sufficiently stable with respect to dissolution and peeling off from the resonator surface. Moreover, this film should be relatively rigid, neither shrinking nor swelling in the test solution. 

Fig. 12.3. Mercury sensor based on surface acoustic waves (SAW) with shear-horizontal acoustic plate mode. This approach was tested in Ref. [8].

A new Pt(II) polyyne polymer, P15, prepared from the reaction of cfs-[Pt(PPh3)2Cl2] with l,4-diethynyl-2,5-dihexadecyloxybenzene using the extended one pot polymerization route, was tested for its sensing properties and showed fast and reproducible response to relative humidity variations and methanol vapor in surface acoustic-wave (SAW) sensors.46 A SAW sensor was fabricated from polymer P15 as a sensitive membrane, and the polymer was deposited as thin film on the surface of SAW delay lines implemented on three different piezoelectric substrates. High sensitivity and reproducibility were recorded for such devices. The acoustic characterization of the polymer film was also studied with the aid of theoretical results obtained by the perturbation theory. 

An electronic tongue based on dnal shear horizontal surface acoustic wave (SH-SAW) devices was developed to discriminate between the basic tastes of sour, salt, bitter, and sweet [57]. Sixty MHz SH-SAW delay line sensors were fabricated and placed below a miniature PTFE housing containing the test liquid. All the tastes were correctly classified without the need for a selective biological or chemical coating. 

This paper consists of a description of design considerations for development of small, hand-held vapor sampling analytical detection devices, some solutions to these design problems, and up-to-date results of testing activities on hand-held devices suitable for CW defense as well as CW destruction applications. Devices based on Ion Mobility Spectrometry and Surface Acoustic Waves are the two technologies discussed. 

Tables 4.3 and 4.4 list several substances that have been used to simulate the nerve agent GB and bhster agent HD, respectively, in detector testing. The listed chemicals in Table 4.3 are similar to GB in some aspects. For example, the structure of dimethyl methylphosphonate (DMMP) is very similar to that of GB. Both contain the CH3-P=0 group. The main difference between them is that the simulant does not have the more active fluoride (-F) function group, and thus, its toxicity is much lower than GB. Both compound molecules contain phosphorous. Therefore, it is possible to use DMMP as a simulant to evaluate the performance of a flame photometric detector, ion mobility detectors, or surface acoustic wave detector.

Many techniques have been developed to measure the Young s modulus and the stress of the mesoscopic systems [12, 13]. Besides the traditional Vickers microhardness test, techniques mostly used for nanostructures are tensile test using an atomic force microscope (AFM) cantilever, a nanotensile tester, a transmission electron microscopy (TEM)-based tensile tester, an AFM nanoindenter, an AFM three-point bending tester, an AFM wire free-end displacement tester, an AFM elastic-plastic indentation tester, and a nanoindentation tester. Surface acoustic waves (SAWs), ultrasonic waves, atomic force acoustic microscopy (AFAM), and electric field-induced oscillations in AFM and in TEM are also used. Comparatively, the methods of SAWs, ultrasonic waves, field-induced oscillations, and an AFAM could minimize the artifacts because of their nondestructive nature though these techniques collect statistic information from responses of all the chemical bonds involved [14]. 

The use of the surface ultrasonic waves seems to be convenient for these purposes. However, this method has not found wide practical application. Peculiarities of excitation, propagation and registration of surface waves created before these time great difficulties for their application in automatic systems of duality testing. It is connected with the fact that the surface waves are weakened by soil on the surface itself In addition, the methods of testing by the surface waves do not yield to automation due to the difficulties of creation of the acoustic contact. In particular, a flow of contact liquid out of the zone of an acoustic line, presence of immersion liquid, availability of chink interval leads to the adsorption and reflection of waves on tlie front meniscus of a contact layer. The liquid for the acoustic contact must be located only in the places of contact, otherwise the influence on the amplitude will be uncontrolled. This phenomenon distorts the results of testing procedure. 

Test methods are used to detect flaws. As an example when flaws or cracks grow in plastic, minute amounts of elastic energy are released and propagated in the material as an acoustic wave. A nondestructive acoustic emission test has sensors placed on the surface that can detect these waves providing information about location and rate of flaw growth. These principles form the basis for nondestructive test methods such as sonic testing. 

Tsukahara, Y., Nakaso, N., Ohira, K and Yanaka, M. (1996). Interaction of acoustic waves with solid surfaces. In Advances in acoustic microscopy, Vol. 2 (ed. G. A. D. Briggs and W. Arnold), pp. 103-65. Plenum Press, New York. [91, 149, 218, 226] Vetters, H Matthaei, A., Schulz, A., and Mayr, P. (1989). Scanning acoustic microprobe analysis for testing solid state materials. Mater. Sci. Engng. A122, 9-14. [199, 207,219]... 

The dependencies described are sufficient for designing the different types of ultrasonic transducers for testing by surface waves. The constant transmission of acoustic energy is provided. 

Fig. 13.17 shows the structure and principle of a T-bumer, as used to measure the response function of propellants. Two propellant samples are placed at the respective ends of the T-burner. The burner is pressurized with nitrogen gas to the test pressure level. The acoustic mode of the burning established in the burner is uniquely determined by the speed of sound therein and the distance between the burning surfaces of the two samples. When the propellant samples are ignited, pressure waves travel from one end to the other between the burning surfaces of the samples. When a resonance pressure exists for a certain length of the T-bumer, the propellant is sensitive to the frequency. The response function is determined by the degree of amplification of the pressure level. 

---